This invention relates generally to tire changing apparatus, and more specifically to tire changing apparatus with the capability of measuring at least one uniformity parameter of a wheel/tire assembly and which incorporates an actuation means for applying a load to the tire of a wheel/tire assembly mounted to the tire changing apparatus, via a load roller assembly during a tire changing procedure.
Much effort has gone into reducing the vibration of wheel/tire assemblies while a vehicle is in motion. Wheel balancers are commonly used to reduce static and dynamic imbalances in a wheel/tire assembly which result in measured vibrations. These systems determine a measure of unbalance in vehicle wheel/tire assemblies by an analysis of the mechanical vibrations caused by rotating the wheel/tire assembly. The mechanical vibrations are measured as motions, forces, or pressures by means of transducers, which convert the mechanical vibrations to electrical signals. Wheel/tire assembly unbalance may result from unbalance in the wheel, unbalance in the tire, or both.
Even when a wheel/tire assembly is properly balanced, such as by the application of imbalance correction weights to the assembly, non-uniformity in the construction of the tire or a runout in the wheel rim can cause significant vibration forces as the wheel/tire assembly rolls across a road surface under vehicle load conditions. Most tire manufacturers inspect their tires on tire uniformity machines and grind surface material off the tires as required to improve rolling characteristics of the tires. Even after this procedure, tires will often produce significant vibration forces (not related to imbalance) of as they roll on a smooth road.
Conventional wheel balancers also have more subtle deficiencies that arise in connection with compensating for run-out and in tire matching. For example, wheel rim runout is frequently measured from the “outside” of the rim (i.e., that portion of the wheel rim that is exposed to view once the tire is mounted thereon. If the wheel rim runout measured on the “outside” portion of the rim does not correspond to the runout of the bead seat surface itself (which is on the “inside”), errors may be introduced in an attempt to match or compensate out-of-round conditions on a tire with the out-of-round conditions on the associated wheel rim by adjusting the rotational position of the tire relative to the wheel rim.
Even if the actual bead seat surface is used to measure runout in a wheel rim, errors can still result. For example, if the bead seat method is used to obtain a measure of rim runout, the rim must be removed from the balancer for mounting the tire and then remounted to the balancer to measure wheel/tire assembly force variations. Any centering difference with respect to the mounting of the rim on the spindle of the balancer will result in errors in the determination of the rim runout, the assembly force variation, and the tire force variation computation. This “centering error” can become even more significant with larger wheel/tire assemblies. Similarly, with conventional wheel balancing equipment, after mounting the tire on the rim, the rim must be mounted at exactly the same angular position relative to the spindle as it was mounted in the rim runout measurement step. Otherwise the angle of the recalled rim contribution will be incorrect and so will the resulting tire computation
In addition to runout, state of the art wheel balancing products measure additional tire uniformity parameters, including lateral forces. Radial ply automotive tires generate lateral forces due to design parameters and manufacturing process variations. It is possible for the lateral forces to have undesirable effect on the vehicle, such as is disclosed in U.S. Pat. No. 6,546,635, herein incorporated by reference.
It should be understood from the above that substantially eliminating wheel/tire assembly vibration is a complex task that conventionally requires a wheel balancer to accomplish. Generally, conventional wheel balancer systems are complex, and relatively expensive pieces of equipment that performs their specific functions well. Conventional wheel balancer systems have a shaft that is used to rotate the wheel/tire assembly, and are generally designed so that the balancer shaft is exactly centered in the center bore hole of the wheel rim. Because it is vitally important for the wheel to be mechanically mounted coaxially to the balancer shaft in order to achieve a good balance, the shaft and other balancer components used in mounting the wheel/tire assembly are all made to extremely tight tolerances.
In contrast, tire changing systems, used to mount and dismount a tire from a wheel rim, are very different from wheel balancer systems, and are designed for a different purpose. As a result, the method for mounting a wheel assembly onto a tire changer is quite different from that used in wheel balancers. Unlike a wheel balancer system which uses a center shaft mounting for balancing purposes, a tire changer system may support the wheel/tire assembly at an edge of the wheel or rim.
There are three reasons for this: (1) the lateral force necessary to unseat the tire bead from the rim bead seat is very high, and it is often advantageous to clamp the rim as close to the bead seat area as possible, and (2) this type of mounting is quicker than mounting through the center hole on a wheel rim, and (3) centering of the wheel/tire assembly on a tire changer is not as critical as it is on a wheel balancer. This mounting method makes it very difficult for the rim's center bore hole to be perfectly centered about the center point of the tire changer rotational means. Because the rim's center bore hole does not perfectly rotate about the rotational center when mounted on a tire changer, an imaginary circle created by the tangent to the outer edge of the center bore hole of the wheel rim furthest away from the center point of the tire changer rotational means is larger than the center bore hole itself.
Modern tire changers are now being developed with center spindles for mounting wheels in much the same manner as wheel balancer systems. A hub face is used to contact the rear surface of the wheel rim that contacts the vehicle hub, with a cone and center shaft used to center and clamp the wheel to the hub face. The reason for this is that wheels are becoming larger in diameter. Therefore it is more difficult, and expensive, to create a device to clamp the wheel near its edge. Since the wheels are more expensive it is also desirable to ensure that the wheel does not become damaged due to clamping. By not clamping on exposed surfaces near the rim edge it is easier to protect the wheel rim. Common wheel balancer clamping accessories, such as cones, cups and flange plates can be used to both clamp and protect the wheel. These parts do not need to made to the tight tolerances that are used on a wheel balancer, but the use of the parts is the same.